An example of previously existing devices which performs the function as the power divider is described on page 72 of Four wheel Drive Vehicles (in Japanese, written by Goro Suzuki, published by Sankaido, Dec. 15, 1982), wherein a hollow shaft for receiving power from the drive device such as an engine is coupled at its output side to a differential device within a transfer case, to which a front wheel drive shaft and an intermediate shaft for a rear wheel drive shaft are also connected. Thus, the input power which the hollow shaft receives from the engine is transformed into rotation, on one hand, of the front wheel drive shaft, and on the other hand, of the rear wheel drive shaft. This rotation is then transmitted to the front wheels and the rear wheels.
When a difference in rotation rates between the front wheel drive shaft and the rear wheel drive shaft arises, the differential device acts to maintain smooth power transmission, whereas when a differential lock becomes necessary, the intermediate shaft is locked by the differential device. This is achieved by a sleeve and spline mechanism. In this structure, since the rear wheel drive shaft is located above the intermediate shaft coaxial with the hollow shaft, the height above ground of the rear wheel drive shaft extending far to the rear of the vehicle can be maintained, which is a particularly great advantage in off-the-road driving.
However, in such a conventional power divider, it is necessary to have the intermediate shaft provided on the rear side of the hollow shaft, which makes the length of the transfer case along the front-rear direction of the vehicle long. This means that in order to accommodate the power divider, the degree of freedom in designing other parts is severely restricted, and also the weight of the vehicle is increased. In addition, the total number of parts is increased by the addition of the intermediate shaft and the bearing for supporting it in the transfer case, and this in turn complicates the work of assembly and supervision of parts.
In contrast to this type of power divider, there are others in which there is no rear wheel drive shaft, but, rather, the intermediate shaft itself is used as the rear wheel drive shaft, which reduces the length of the transmission system along the front-rear direction of the vehicle, and the number of parts is reduced. However, the height above ground of the rear wheel drive shaft extending far to the rear of the vehicle cannot be maintained enough, which raises the problem of impaired performance in off-the-road travel, which is one of the main purposes of a four-wheel drive vehicle.